Its not like the normal pokemon games. You get to be a Male/Female hero (who always has his eevee with him until towards the end or if you change the pokemon befriended though its not recommended). But anyways you must go around the region and conquer other castles. You can gather other pokemon and pokemon conquerors. Your ultimate goal is to defeat the owner of Zekrom, that not it but thats the main game i wont ruin the rest for you. More information here.